It is known that vermiculite ore, a type of layer mineral (and other layer-silicate minerals containing vermiculite layers, e.g., hydrobiotite or chlorite vermiculite), can be delaminated and then sheared to form an aqueous dispersion of tiny particles or platelets of vermiculite known as vermiculite lamellae. It is also known that such dispersions of vermiculite lamellae can be used to fabricate shaped articles or products such as paper, sheets, films, rigid foams or composites with other fibrous materials. Such processes for delamination of vermiculite ore and product fabrication therefrom are set forth, for example, in U.S. Pat. Nos. 4,608,303; 4,472,478; 4,271,228; 3,791,969; 3,434,917; 3,325,340 and G.B. Pat. Nos. 2,007,153; 1,585,104; 1,119,305 and 1,076,786;
Articles composed wholly of vermiculite ore particles or composites comprising vermiculite ore particles possess a degree of structural integrity and such useful properties as high heat resistance making them particularly suited for use, for example, as thermal insulation materials, fireproof covering and packaging material and refractory-facing materials.
Notwithstanding such advantageous and useful properties, however, commercial uses of vermiculite articles have been limited by their poor resistance to water dispersibility as such articles tend to disintegrate after prolonged immersion. Various methods have been proposed to impart resistance to water dispersibility in vermiculite products wherein structural integrity of the vermiculite lamellae framework is maintained in aqueous media over long periods of time. Such methods typically propose the addition of "wet-strength" improvers to dispersions of vermiculite lamellae or the incorporation of such wet-strength improvers into articles formed therefrom. These methods include, for example, post-fabrication treatment of vermiculite articles with aqueous solutions of electrolytes, B.P. No. 1,016,385 and B.P. No. 1,593,382, and U.S. Pat. No. 4,608,303; and the post-fabrication treatment of such articles with ammonia vapor or the vapor of an organo amine compound, U.S. Pat. No. 4,219,609. Other methods include treatment of dispersions of vermiculite lamellae used to form products with solutions of inorganic ions, U.S. Pat. Nos. 4,269,628 and 4,497,869; the incorporation of a source of ammonia or ammonia ions, preferably urea, into a dispersion of vermiculite lamellae, U.S. Pat. No. 4,539,046; and the incorporation of a urea-formaldehyde or melamine-formaldehyde resin into a dispersion of vermiculite lamellae, U.S. Pat. No. 4,485,203.
Such methods, however, have been found to be less then satisfactory as they either involve tedious and expensive post treatment and/or curing of formed articles or require the incorporation of large quantities of organic materials which often degrade the desirable high temperature properties of articles comprising vermiculite. Processes which rely on treatment with inorganic ions or electrolytes are further undesirable in that wet strength properties provided by such processes can be severely diminished in the presence of exchangeable or competing ions.